Chemical analysis of liquids, such as water, milk and biological fluids is often desirable or necessary for health maintenance and diagnostic care. Various compositions and elements to facilitate such analyses are known. Such compositions and elements generally include a reagent composition for determining a substance under analysis, identified as an "analyte" herein. The analyte can be a living organism or a nonliving chemical substance. The reagent composition, upon interaction with the analyte, provides a detectable change (e.g. dye formation).
Recently, much work has been directed to developing compositions and elements which are useful for rapid and highly quantitative diagnostic or clinical analysis of biological fluids such as whole blood, serum, plasma, urine and the like.
For example, for the rapid and effective diagnosis and treatment of infectious diseases, it is desirable to be able to detect the bacteria causing the disease as rapidly as possible. Infections of the urinary tract are among the most common bacterial diseases, second in frequency only to infections of the respiratory tract. In fact, in many hospitals, urinary tract infections are the most common form of nosocomial infections, often following the use of in-dwelling catheters and various surgical procedures. Most urinary tract infections (UTI) result from ascending infection by microorganisms introduced through the urethra and vary in severity from an unsuspected infection to a condition of severe systemic disease. Such infections are usually associated with bacterial counts of 100,000 (10.sup.5) or more organisms per ml of urine, a condition referred to as significant bacteriuria. Under normal conditions, urine is sterile, although contamination from the external genitalia may contribute up to 1,000 (10.sup.3) organisms per ml in properly collected and transported specimens.
A significant advance in the detection of microorganisms and other analytes capable of reducing a reducible compound is described and claimed in copending and commonly assigned U.S. Ser. No. 824,766, filed Jan. 31, 1986 by Belly et al and entitled REDUCIBLE COMPOUNDS AND ANALYTICAL COMPOSITIONS, ELEMENTS AND METHODS UTILIZING SAME, now U.S. Pat. No. 4,857,271. The assay described in that application utilizes reducible compounds which release a detectable species in the presence of the analyte. While providing a highly advantageous assay, the reducible compounds described therein generally have limited solubility in aqueous solutions. Hence, water-solubilizing surfactants must be used in the practice of the Belly et al invention to prepare compositions of the reducible compounds.
The use of surfactants in such compositions has serious drawbacks. Surfactants tend to lyse certain cells (e.g. white blood cells) thereby making it difficult to detect or identify such cells. Hence, there is a need in the art for a rapid and highly sensitive assay using reducible compounds which avoids the use of surfactants.